Imaging optical system and projection exposure system including the same

Abstract

An imaging optical system has a plurality of mirrors. These image an object field in an object plane into an image field in an image plane. In the imaging optical system, the ratio of a maximum angle of incidence of imaging light) on reflection surfaces of the mirrors and an image-side numerical aperture of the imaging optical system is less than 33.8°. This can result in an imaging optical system which offers good conditions for a reflective coating of the mirror, with which a low reflection loss can be achieved for imaging light when passing through the imaging optical system, in particular even at wavelengths in the EUV range of less than 10 nm.

What is claimed is: 
     
       1. An imaging optical system which during operation directs light along a path from an object plane to an image plane to image an object field in the object plane into an image field in the image plane, the imaging optical system comprising:
 a plurality of mirrors arranged to direct the light along the path, 
 wherein:
 the imaging optical system is a catoptric imaging optical system, 
 among all mirrors of the imaging optical system which are arranged to direct the light along the path, there are only two mirrors without an opening that intersects the path, 
 for each mirror of the plurality of mirrors, the light is incident on a mirror surface of the mirror at over a range of incident angles including a maximum angle of incidence, and 
 a ratio of the maximum angle of incidence to an image-side numerical aperture of the optical imaging system is less than 33.8°. 
 
 
     
     
       2. The imaging optical system of  claim 1 , wherein the plurality of mirrors includes at least one mirror having an opening for passage of the light, where the opening obscures a pupil of the imaging optical system. 
     
     
       3. The imaging optical system of  claim 2 , wherein the plurality of mirrors comprises six mirrors including at least three mirrors that have openings for the passage of the light that obscure a pupil of the optical imaging system. 
     
     
       4. The imaging optical system of  claim 2 , wherein the plurality of mirrors comprises six mirrors and exactly four of the plurality of mirrors have openings for the passage of the light that obscure a pupil of the imaging optical system. 
     
     
       5. The imaging optical system of  claim 1 , wherein the plurality of mirrors includes at least one mirror having an opening for passage of the light, the opening obscures a pupil of the imaging optical system, and each of the mirrors carries a reflective coating for light with a wavelength which is less than 10 nm. 
     
     
       6. The imaging optical system of  claim 1 , wherein each of the mirrors carries a reflective coating for the light, and each of the mirrors has an average reflectivity greater than 50% for the light at a wavelength which is less the 10 nm. 
     
     
       7. The imaging optical system of  claim 6 , wherein the mirrors have an average reflectivity greater than 58% for the light with a wavelength of 6.9 nm. 
     
     
       8. The imaging optical of  claim 1 , wherein, for light having a wavelength which is less than 10 nm, the imaging optical system resolves structures in the image field having a dimension of 20 nm or less, and the imaging optical system is a catoptric imaging optical system for a projection exposure system for microlithography. 
     
     
       9. The imaging optical system of  claim 8 , wherein the imaging optical system resolves structures in the image field having a dimension of 16 nm or less. 
     
     
       10. The imaging optical system of  claim 8 , wherein the imaging optical system resolves structures in the image field having a dimension of 11 nm or less. 
     
     
       11. The imaging optical system of  claim 8 , wherein the imaging optical system resolves structures in the image field having a dimension of 8 nm or less. 
     
     
       12. The imaging optical system of  claim 8 , wherein the imaging optical system resolves structures in the image field having a dimension of 6 nm or less. 
     
     
       13. The imaging optical system of  claim 1 , wherein the imaging optical system has an image side numerical aperture of 0.5 or less and resolves structures in the image field having a dimension of 20 nm or less, and the imaging optical system is a catoptric imaging optical system for a projection exposure system for microlithography. 
     
     
       14. The imaging optical system of  claim 13 , wherein the imaging optical system resolves structures in the image field having a dimension of 16 nm or less. 
     
     
       15. The imaging optical system of  claim 13 , wherein the imaging optical system resolves structures in the image field having a dimension of 11 nm or less. 
     
     
       16. The imaging optical system of  claim 13 , wherein the imaging optical system resolves structures in the image field having a dimension of 8 nm or less. 
     
     
       17. The imaging optical system of  claim 13 , wherein the imaging optical system resolves structures in the image field having a dimension of 6 nm or less. 
     
     
       18. A system, comprising:
 the imaging optical system of  claim 1 ; 
 a light source; and 
 an illumination optical assembly; 
 wherein during operation the illumination optical assembly direct light from the light source to the object field of the imaging optical system and the system is a projection exposure system for microlithography. 
 
     
     
       19. The system of  claim 18 , wherein the light from the light source has a wavelength which is less than 10 nm. 
     
     
       20. A method for the production of a microstructured component, the method comprising:
 providing a reticle and a wafer in a system; 
 projecting a structure on the reticle onto a light-sensitive layer support by the wafer using the system; and 
 producing a microstructure on the wafer after projecting the structure, 
 wherein the system comprises:
 the imaging optical system of  claim 1 ; and 
 an illumination optical assembly, and 
 
 wherein during operation the illumination optical assembly directs light from a light source to the object field of the imaging optical system. 
 
     
     
       21. The imaging optical system of  claim 1 , wherein at least one of the plurality of mirrors comprises a coating which comprises boron carbide. 
     
     
       22. The imaging optical system of  claim 1 , wherein at least one of the plurality of mirrors comprises a coating which comprises a plurality of B 4 C/CsI bilayers. 
     
     
       23. The imaging optical system of  claim 22 , wherein a thickness of an individual bilayer increases parabolically with increasing distance of the bilayer from an optical axis of the imaging optical system. 
     
     
       24. An imaging optical system which during operation directs light along a path from an object plane to an image plane to image an object field in the object plane into an image field in the image plane, the imaging optical system comprising:
 a plurality of mirrors arranged to direct the light along the path, 
 wherein:
 wherein at least one of the plurality of mirrors comprises a coating which comprises a plurality of B 4 C/CsI bilayers, 
 the imaging optical system is a catoptric imaging optical system, 
 for each mirror of the plurality of mirrors, the light is incident on a mirror surface of the mirror at over a range of incident angles including a maximum angle of incidence, and 
 a ratio of the maximum angle of incidence to an image-side numerical aperture of the optical imaging system is less than 33.8°. 
 
 
     
     
       25. The imaging optical system of  claim 24 , wherein a thickness of an individual bilayer increases parabolically with increasing distance of the bilayer from an optical axis of the imaging optical system.